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DOI: 10.1055/s-0033-1340765
Isochromenes Synthesis by Cyclization and Asymmetric Transfer Hydrogenation
Chiral Copper(II) Phosphate Catalyzed Enantioselective Synthesis of Isochromene Derivatives by Sequential Intramolecular Cyclization and Asymmetric Transfer Hydrogenation of o-Alkynylacetophenones.
Angew. Chem. Int. Ed. 2013;
52: 13284-13288
Publication History
Publication Date:
17 February 2014 (online)
Significance
Asymmetric counteranion-directed catalysis (ACDC) has emerged as a powerful strategy to induce asymmetry in reactions that proceed through cationic intermediates (see Review below). In this report, asymmetric transfer hydrogenation of transition-metal-containing carbonyl ylides is achieved using a Hantzsch ester as hydrogen source and a chiral binaphthyl phosphate as chiral counteranion. The method provides access to enantiomerically enriched isochromenes.
Rewiew: M. Mahlau, B. List Angew. Chem. Int. Ed. 2013, 52, 518–533.
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Comment
The key chiral ion pair 1a is generated via a copper(II)-catalyzed 6-endo-dig cyclization of ketone 1. The ligand on copper (X*) is believed to be a chiral phosphate generated in situ from the corresponding phosphoric acid 2 in the presence of base. When a preformed and isolated copper(II)/phosphate complex was used in the reaction, the desired product was formed with comparable yield and er.
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